Atmospheres on Nonsynchronized Eccentric-tilted Exoplanets. I. Dynamical Regimes

Abstract

Relatively long-period, nonsynchronized planets—such as warm Jupiters—potentially retain the primordial rotation, eccentricity, and obliquity that might encapsulate information on planetary climate and formation processes. To date, there has not been a systematic study on climate patterns on these planets that will significantly influence their observations. Here we investigate the atmospheric dynamics of nonsynchronized, fast-rotating exoplanets across various radiative timescales, eccentricities, and obliquities using a shallow water model. The dynamical pattern can be demarcated into five regimes in terms of radiative timescale τ rad and obliquity θ . An atmosphere with τ rad shorter than a planetary day usually exhibits a strong day–night temperature contrast and a day-to-night flow pattern. In the intermediate τ rad regime between a planetary day and a year, the atmosphere is dominated by steady temperature and eastward jet patterns for θ  ≤ 18° but shows a strong seasonal variation for θ  ≥ 18° because the polar region undergoes an intense heating at around the summer solstice. If τ rad is larger than a year, seasonal variation is very weak. In this regime, eastward jets are developed for θ  ≤ 54° and westward jets are developed for θ  ≥ 54°. These dynamical regimes are also applicable to planets in eccentric orbits. The large effects of exoplanetary obliquities on circulation patterns might offer observational signatures, which will be investigated in Paper II of this study.